Reproductive Structures in Flowering Plants Flowers Reproductive shoots of sporophytes Flowering plants make sexual spores in male stamens and female carpels of floral shoots Gametophytes develop from the spores Pollen grains contain male gametophytes Ovules contain female gametophytes

Flowering Plant Life Cycle and Floral Structures

Coevolution Flowering plants coevolved with pollination vectors that transfer pollen from stamens to carpels of flowers of the same species Pollinators receive nectar and pollen

Attracting Pollinators

From Gametophyte to Fertilization Male gametophyte formation Pollen sacs form in anthers of stamens Haploid microspores form by meiosis of diploid spore-producing cells Microspore develops into a sperm-bearing male gametophyte, housed in a pollen grain

From Gametophyte to Fertilization Female gametophyte formation A carpel’s base has one or more ovaries Ovules form from the inner ovary wall One cell in the ovule (haploid megaspore) gives rise to the mature female gametophyte One cell of the gametophyte becomes the egg

From Gametophyte to Fertilization Pollination Arrival of pollen grains on a receptive stigma Germination Pollen grain forms a pollen tube (two sperm nuclei inside); grows through ovary to egg Double fertilization One sperm nucleus fertilizes the egg, forming a zygote; one fuses with the endosperm mother cell

From Zygote to Seed and Fruit A mature ovule: Embryo sporophyte and endosperm inside a seed coat Eudicot embryos have two cotyledons; monocot embryos have one Fruit Seed-containing mature ovary (and accessory tissues)

Embryo Development: Eudicot

From Flowers to Fruits

remnants of sepals, petals ovary tissue seed enlarged receptacle Fig. 28.7d, p.461

Fruits: Seed Dispersal Fruits help seeds disperse by adaptations to air or water currents, or diverse animal species

The Plant Body Aboveground shoots Roots Stems that support upright growth Photosynthetic leaves Reproductive shoots (flowers) Roots Typically grow downward and outward in soil

shoot tip (terminal bud) young leaf flower lateral (axillary) bud node internode dermal tissue vascular tissues leaf seeds in fruit withered seed leaf (cotyledon) ground tissues SHOOTS ROOTS stem primary root lateral root root hairs root tip root cap

Epidermis

Leaf Structure Between upper and lower epidermis Stomata Mesophyll (photosynthetic parenchyma) Veins (vascular bundles) Stomata Openings in cuticle-covered epidermis that control passage of water vapor, oxygen, and carbon dioxide

leaf vein (one vascular bundle) xylem phloem cuticle upper epidermis palisade mesophyll Water, dissolved mineral ions from roots and stems move into leaf vein (blue arrow). spongy mesophyll lower epidermis Photosynthetic products (pink arrow) enter vein, will be distributed through plant. epidermal cell stoma (small gap across lower epidermis) Oxygen and water vapor (blue arrow) diffuse out of leaf through stomata. Carbon dioxide (pink arrow) in outside air diffuses into leaf through stomata.

Water Conservation Cuticle Waxy covering that protects all plant parts exposed to surroundings Helps the plant conserve water

Water Conservation Stomata Gaps across the cuticle-covered epidermis Closed stomata limit water loss (but prevent gas exchange for photosynthesis and aerobic respiration) Environmental signals cause stomata to open and close

How Stomata Work A pair of guard cells defines each stoma Water moving into guard cells plumps them and opens the stoma Water diffusing out of guard cells causes cells to collapse against each other (stoma closes)

guard cell guard cell chloroplast (guard cells are the only epidermal cells that have these organelles) stoma 20 µm Fig. 27.10, p.448

Effects of Pollution on Stomata

Complex Vascular Tissues Xylem Vessel members and tracheids are dead at maturity; their interconnected walls conduct water and dissolved minerals Phloem Sieve-tube members are alive at maturity, form tubes that conduct sugars Companion cells load sugars into sieve tubes

one cell’s wall sieve plate of sieve tube cell pit in wall companion parenchyma fibers of sclerenchyma vessel of xylem phloem Fig. 26.8, p.429

Vascular Bundles Bundles of xylem and phloem run through stems Monocot stems: Vascular bundles distributed through ground tissue Herbaceous and young woody eudicots: Ring of bundles divides ground tissue into cortex and pith Woody eudicot stems: Ring of bundles becomes bands of different tissues

How to distinguish between monocots and dicots Stem Monocot-randomly distributed vascular bundles Dicot--ring of vascular bundles Leaf Monocot--parallel veins Dicot--branched veins Flowers Monocot--petals in 3’s Dicot--petals in 4’s or 5’s

Primary Structure of Eudicot and Monocot Stem

Eudicot and Monocot Leaves and Vein Patterns

Transpiration and Cohesion-Tension Theory Evaporation of water from plant parts (mainly though stomata) into air Cohesion–tension theory Transpiration pulls water upward through xylem by causing continuous negative pressure (tension) from leaves to roots

Cohesion and Hydrogen Bonds Hydrogen bonds among water molecules resist rupturing (cohesion) so water is pulled upward as a continuous fluid column Hydrogen bonds break and water molecules diffuse into the air during transpiration

Root Functions Roots Absorb water and mineral ions for distribution to aboveground parts of plant Store food Support aboveground parts of plant

Roots Roots absorb water and mineral ions Root hairs Expand through soil to regions where water and nutrients are most concentrated Root hairs Greatly increase root absorptive surface

Root Symbionts Draw products of photosynthesis from plants Give up some nutrients in return Mycorrhizae (fungal symbionts) Increase mineral absorption Root nodules (bacterial symbionts) Perform nitrogen fixation

Root Nodules

Dendroclimatology Wood cores and climate history

Processes of Survival Plants and animals adapted in similar ways to environmental challenges Gas exchange with the outside environment Transportation of materials to and from cells Maintaining internal water-solute concentrations Integrating and controlling body parts Responding to signals from other cells, or cues from the outside environment

Rhythmic Leaf Movements

Responses to Environment: Thigmotropism In some plants, direction of growth changes in response to contact with an object

28.9 Biological Clocks Internal timing mechanisms respond to daily and seasonal cycles Circadian rhythms (24-hour cycle) Solar tracking